Abstract

The complex where we used the materials ins this study, explores iron ore in an open pit process and is formed by a significant number of mines, and all their geotechnical structures such as waste rock stackings, tailings dams and, recently, the stackings that are being constructed with waste rock and tailings. For the piles formed by the shared disposal of waste rocks and filtered tailings, the characterization of the materials and the strength and critical state parameters determined the executive methodology and the safety factors required for the projects. The waste rocks and filtered tailings are mechanically disposed and divided into zones defined not only according to the geotechnical characteristics of the materials, but also the structural and operational needs of the stacking, which are divided into the confining zone and the confined zone. In the confining zone, compacted waste is deposited. The aim of this procedure is to enhance the structural performance by employing materials with higher resistance. In the confining zone, as closer to the outer layer of the pile, greater shear strength is mobilized. In the confined zone, friable waste, and mining tailings are disposed. In this zone, there is less mobilization of shear strength. For tailings, control and evaluation adhere to parameters outlined by the Critical State Line, employing the void ratio control of layers. This ensures dilatant mechanical behaviours for all confinement stresses specified in the project.

Abstract

Dry stacking of filtered tailings has become feasible due to the development of novel dewatering technologies. It offers an alternative to address the safety-related issues associated with conventional slurry disposal in reservoirs confined by upstream heightened dams. The operation and maintenance of such structures are challenging because of the high degree of uncertainty inherent in this material due to its spatial variability in state and gradation. It is also susceptible to liquefaction when saturated and in a loose state. In contrast, the filtered tailings can be compacted and piled up to hundreds of meters to meet prescribed design requirements. Eventually, a cementing agent can be incorporated into the tailings before compaction to enhance the general engineering properties. Nevertheless, few dry-stack facilities operate; none use cement as a stabilising agent. Accordingly, this paper assesses the mechanical response of artificially cemented iron ore tailings compacted in the field to form an experimental pile. Plate load tests and cone penetration tests were used. The experimental pile was divided into four sections, each compacted with different combinations of roller passes (4 or 6 passes) with and without vibration frequency. The results showed that the compacted material was practically insensitive to variations in compaction parameters, as evidenced by similar results in the tested sections' stress-strain responses and cone tip strength values. This study also highlights the effectiveness of field testing in investigating the response of stacking plants and the importance of using a small amount of cement to achieve adequate mechanical performance.